High-frequency signaling



Nov. 5, 1929., B.' w. KENDALL 1,734,132 I HIGH FREQUENct SIGNALING ,Filed sept. 22; 1916 2 sheets-sheet `1 Nov. 5k,

B. W. KENDALL HIGH FREQUENCY SIGNALING 2 Sheets-Sheet A 2 Filed Sept. 22, 1916 Patented Nov.l 5, 1929 UNITED STATES PATENT; oFFlcEff,

BURTON W. KEHDALL,

PANY, INCOPORATED, 0F YORK, N. -Y., ACORPBATION 0F vNEW YORK HIGH-FREQUENCY vS'IGN'ALING' Application inea september 22,1916. serial No. 121,571. l

This invention relates to high frequency signaling, and more particularly to the relaying of messages, and has for an object to prevent a local circulation of power, or singing, at a relaying station. t

. The invention provides for receiving a modulated wave having a certain carrier frequency, and in combining Athis modulated wave with locally generated oscillations to change the carrier frequency. Since the carv rier frequency has been changed to a-value to which the local receiving system is not receptive, the new carrier wave will be sent to the distant station and will not be received by the local receiving system.

The-invention also provides for successively repeating almessage by using a plurality of such repeating stations and by changing to a dierent frequency at each repeating station.

This will be better understood by considering the composition of a modulated carrier wave. lf high frequency carrier oscillations are modulated or caused to vary in amplitude in accordance with the wave form of low frequency signal oscillations, the modulated carrier wave of varying amplitude is not a simple sine wave, but is complex in form. This modulated carrier wave may, however, be resolved into an unmodulated component or a carrier wave of constant amplitude anda modulated component comprising two waves Whose frequencies are the sum and difference respectively of the carrier and signal frequencies. l

lf l? isthe carrier frequency and a the signal frequency, and if the carrier frequency 'has been modulated in accordance with the form ofthe signal wave, the modulatedcarrier wave may be. resolved into three simple sine waves whose frequencies are P, Pa, P+ a. It is to be understood that arepresents .either a single frequency useful in telegraphie signaling or the instantaneous frea quency value of a modulating speech wave used in telephone' si naling.

A demonstration hat a modulated carrier wave may be so Vresolved is contained in the patent to Arnold 1,449,372, lgranted Mzwch 27, 1923, `on application Serial No. 64,502, filed December 1, 1915. j 'p 011- maw4 Yoaxg'N. Y., AssIGNoR l1ro WESTERN ELECTRIC com- According to this invention a modulatedl l wave having a carrier frequency P is received at a repeating station. This is combined with locally generated oscillations of the high frequncy g to produce sum and difference fren,

quencles in a manner similar to the' method of modulation explained above. Thusthe side frequency P-I-a combines with the frequency 'gto produce the frequencies q-l-P-l-a and vg-P-a, and the side frequency P'-a similarly gives the frequencies g+.P-aand g-P-la. Thus it is possible to repeat a modulated higlrfrequency component at a fre. quency different from that at Xwhich it is receivedby combining other carrier oscillations 1 therewith in a manner similar tothe method v.of modulating a carrier wave in' accordance with the signal wave. lf it is desired to repeat at an increased carrier frequency, the circuit is tuned to transmit oscillations of frequency +P) La.v rllhedouble sign (i) as used in t is specification is to, be read in the ordinaryy disjunctive sense, that is, plus or minus. lt may, however, in general, un-

less the context indicates otherwise,- be read in the concomitant sense, that is,,plus' andv minus it bein stated hereinafter that either one or bothv si e frequencies of a modulated wave may be raised or lowered in frequency in accordance with the present invention. ln-

asmuch as the unmodulated carrier component may or may not be suppressed or may be partly suppressed as hereinafter stated, 1t

'willbe understood that energy of the unmodulatedcarrier frequency may or may not Y be present when both side bands'are transmitted. For instance, if a modulatedcomponent of carrier frequency"50,000 is utlllzed to modulate carrier oscillations of 10,000,

there is available for transmission a modulated component of carrier oscillations of fre-4 quency 60,000. Of course, the carrier frequency may be doubled by making g=P.

The modulated component received at va receivig station may be amplified and detected by 'mbining it with locally generatedoscil'- lations of the carrier frequency accordmgto the homodyne method disclosed in U. S. pat-A ent to Carson1,449,382 granted March 27,

1923, on application Serial No. 64,524 filed serves to vDecember 1*, 1915.

If it is desired to repeat the modulated componentl of the carrieroscillations at a frequenc lower than that at which they are receive the sending circuit may "be tuned to transmit the modulated component of frequency (g-P) ia. For instance, if the mod-l ulated component of carrier frequency 60,000

lo 'were received, this might be combined with 5 bythe time they parison to This results 1n new side frequencies, each' spectively of gL-a has been transmitted that t carrier oscillations of frequency 20,000 in which case a modulated component of carrier oscillations of frequency 40,000 may be sei lected by a tuned circuit and transmitted.

These two steps, or any combination of them, for increasing and lowering the carrier frequency, may be used in conjunction for the successive repetition of signals, or the carrier frequency may be changed but once, as desired. y

It will be apparent that after any side frency which may be represented b P -lor e amplitude of these oscillations will be very small have reached a distant receiving stationr\` One or both of these side frequencies however, is combined with carrier oscillations of frequency (l, the amplitude of which may be very large in comthe feeble oscillations received.

having as components the componentsvof the originalv unmodulated wave, that is, side frequencies equal to the sum and difference rethe incoming oscillations and the locally produced carrier oscillations. Accordingly, the upper side frequency (-P-t-g) ia produced by the combination of the localv oscillations of frequency g with the 40 incoming wave and alsothe lower side frequency (P-g) ia have amplitudes which are large in comparison to the amplitude of the received oscillations, so that this scheme of modulation serves not only to change the carrier frequency, but also to increase the energy of the modulated component. Therefore there may be transmitted from the combining device a modulated component which has more energy' than the one rev ceived. Such a side frequency wave may be used at any place where it exists to repro- -duce the signal representedby the original [y modulating wave in the manner specified in lCarson Patent 55 Further am liieation may be secured by o5 ceiving stations;

. station; Fig. 2 indicates 1,449,382 mentioned above.

, using ampli ers.

v For a detailed description of a system which provides a method and means for practicing this invention, reference may-be made 604 to the drawings in which Fig. 1 shows diagrammatically the circuit arrangement for using the scheme of modulation at a repeating a plurality of rebetween the sending and repeating stations Fig. 3 isla circuit diagram Vment vacuum of a repeating` and monitoring station which wave; Figs. 4 and 5 are forms of receiver circuits which may be used for detecting and' indicating the signal modulated waves at a re ceiving station, such. as the station Z; and Fig. 6 illustrates the application of the invention to a wire line system for repeating, amplifying and changing the frequency of carrier Waves any desired number of times in transit between the signal initiating station lV vand the inal receiving station Z.

In Fig. 1 the antenna 1 is tuned to receive either the side frequency P-l-a or the side frequency P-a' transmitted from a distant station atV which the remaining side frequency and the unmodulated carrier frequency l? may ormay not have been suppressed, as desired. As stated in ICarson Patent 1,449,372 above referred to, better quality of received signals and more economical usev of power at the transmitting station may be secured by transmitting only a single side frequency, for example, P a. However, both side bands either with or without the unmodulated carrier component may be transmitted in accordance with the present invention with excellent results. As explained in Carson Patent 1,449,372, suppression of the unmodulated component makes it desirable, but not essential, that an unmodulated com ponent be introduced and combined with the modulated component before detection. The antenna l and the local generator 2 of oscillations of frequency g are inductively connected to the' input circuit of modulator 3, by means of the transformers 4 and 40, respectively. The modulator 3 is a three-ele; tube'of the audion type, and comprises an evacuated vessel which en'closes the cathode filament 5, grid 6 and anode or double the frequency of a carrier supplied by battery 11 through impedance coil 12.

Asis characteristic of all vacuum tubes of the audion type, so is it true of the modulator 3, that therelation between the input voltage and the output current is non-linear, or successive small increments of voltage applied tothe input circuit do not produce proportional increments in the output current. Accordingly, the tube is acdistorting device and may be said to have a curved characteristic. Such a characteristic is essential in order that the sum and ldifference frequencies may be obtained."

, If, in the-sending, the suppression of the unmodulated component has been incomplete, beatsv of signal frequency a will be present `in the modulator output circuit. Tlns serves as a convenient means of observing the signal by detecting and Aindicattance serves to keep the high frequency oscillations out of the receiver circuit.v Condenser lshuts out thelow' frequency oscillations from the modulator output circuit which lis inductively .connected through transformer 17 to the input'circuit of arnlifier 18 of the audion type. Eer a detailed tions vof frequency 1', furnished by generator escription of the operation of the audion type amplifier, reference may be made to Arnold Patent 1,129,942, March 2,1915. The amplier'18 is a three-element vacuum tube similar in structure.- to the modulator. -The amplifier input circuit is tuned by variable condenser 19 and the outputV circuit is inductively connected to. the input circuit vof another amplifier 21 similar to'- amplifier. 18,

by transformer 20. The space current in the amplifier output circuits is supplied by batteries 22 and 23. The input circuit of amplifier 21 may. be tuned by variable con denser 24, and its output circuit is inductively related to sending antenna 25 by means of transformer 26.v i

It is evident that a side frequency P ia is received by antenna 1 and combined with locally generated oscillations of frequency g supplied by generator 2; the side frequency (P i (1) ia may then be selected by the tuned circuits, ampli fied, and transmitted from antenna 25. Sinwe the sending antenna transmits carrier oscillations of'a frequency different from the frequency for which antenna 1 is tuned, the outgoing energy Will not affect the local receiving apparatus.

In Fig. 2 it is shown hoW the carrier frequency may be increased at one repeating station and subsequently lowered at another repeating station. -In this ligure, W represents a sending station, Z a receiving station, and X and Y intermediate repeating stations. The circuit arrangement at stations vX and Y is substantially the lsame, as `that shown in Fig. 1, the only difference being in the tuning of the circuits and the frequency of the generators. As to Figsf 1 and 2, it is obvious that the location of the'modulatorrand one of the amplifiers may be interchanged so that'th'e signals may be amplified before they are modulated. It maybe -desirable to-amplifyrst to intensify the effect in the monitoring circuit.

ln Fig. 2,'antennae 11, 12 and 251, 25.2-, Correspond respectively to receiving antenna 1 and sending antenna 25 of Fig. 1. Also the generators 21 and 22 at stations X'and Y respectively correspond to .generator 2,1

Y' Fig. `1. ltstations X and Y the connections` of the modulatofand ampliiiersare the same 1 F' met asin rig, 1, @indicated-by the lines. A-A, B-'-B, O-C, D-D, E-E, E-F.

At station W there is supplied a modulated Wave which is transmitted and received by antenna 1 l'at repeating station X. Here the' sidev frequency Pia is combined with carrier oscillations of frequency g, delivered by 'generator 21. If it is desired to increase the lcarrier frequency, the side frequency (Pig) ia is selected by the tuned circuits,

amplified and transmitted from sending' antenna 25. If it is then desired to llower the carrier frequency, the side frequency (P-I-g) ia is combined with carrier oscilla- 22 at stationf Y, and the side frequency (P+q-r) i-a is selected by the tuned cir- X receives a frequency 40,000ia and sends Y receives a frequency 701,000ia and sends a frequency .55,000ia.

So that X sends at a frequency different from that at which X receives and Y sends at a frequency different from that receivedl by both X andl Y.l This prevents a local circulation of power and thereby prevents singing.

Fig. 3 is a circuit diagram of a repeater station at which the cartier frequency is to be doubled. The apparatus of this station consists of the same elements as the elements ,of

4F ig. l combined in the ,same manner. The,

incomin hi h fre uency energy may comprise colpoligents ofl frequency P, P a, P a. or the unmodulated carrier frequency component P may be suppressed. But if -desired the carrier and one side frequency may be suppressed. Local source 2 has the frequency of the incomingcarrier that is f=P. The

outgoing lWave will consist of the components of the modulated wave which are received with the' carrier doubled thatis, 2P, as indicatedon the drawing. IIn this arrangement,

owing to the fact that the local carrier freexample, P 40,000, g 30,000

quency is the same as the incoming carrier P and preferably of large amplitude, the signal reproduced in the receiver 13 will beof eX lcellent quality, Whether the unmodula-ted carrier component has been Wholly or partlyl suppressed at the transmitter-or not. If it is found convenient to double. thecarrier frcquency the repeater station of Fig. 3 maybe employed Wherever the arrangement of Fig.A 1 is suitable. lIncoming and outgoing lines may be substituted for the antennae 1 and 25 respectively, if the station 3 is used in a Wire v,system instead of a radio system. v

4 is ay diagram of a receiving c1rcu1t may be used to receive' modulated waves consisting of one side frequency alone or both side frequencies with or Without an unmodulated component. The receiving antcnna 31 is preferably tuned to the same frequency as the -transmitting antenna at thestation from which signals are to be received. In line Wire systems the incoming line takes the place of the antenna 31. Oscillation, circuit 32 is preferably tuned to the same frequency as the antenna 31. Connected across the condenser 33 ofcircuit 32 is the input circuit of amplifier 34 4of the well known three-element vacuum tube type of frequency of the incoming wave.

fa receiving device 41 such as a telephone receiver.

Fig. 5 is a receiving circuit similar to the circuit. of Fig. 4 in which the amplifier 34 and the tuned circuit 32 are omitted. This) receiving -circuit and its mode of operation are, otherwise identical with the correspondsystem in ingly numbered parts of the arrangement of Fig. 4. I

ig. 6 diagrammatically illustrates a wired which the scheme of changing the of a local source carrier frequency by means 4is applied in amplifying and repeating circuits placed at suitable intervals along the `line between the station W where the transmitting signals originate` and a receiving station Z. In this system the repeating'stations are connected by conductive circuits instead of radio links consisting of pairsof antennae, one of which radiates energy to be received by thel other. The carrier wave may have' its frequency stepped up or down or doubled at each station in the system o`r it may be changed 1n any of these ways at a particular station regardless of the change 5, which has occurred at the preceding station.

carrier waves of v100,000 cycles For example',

dance with speech which modulated in accor "originate at the station W may be stepped down to 480,000'cycles by means of a local Vsource 21 of 20,000 ycleslat the stationX.

The 80,000 cycle waves may 1n turn be stepped down to 65,000 cycles. by means of ay local 4sourcefQ2 `of 15,000 cycle frequency at the lto station Y'. The 65,000 cycle waves may then be transferred over'the line from the station Y tothe station Z and there used to reproduce` signals by means of any receiver circuit such as the circuits of Figs. 4 or 5. Monitoring apparatus such as is used in the arrangements of Figs. 1 and 3 maybe used at ea'chrrepeat.- ing station to listen to the signal and thereby observe the transmission:

closed, it 1s to -tion is not to Yceiye a modulated wave,

- It is obviously immaterial as to the manner in which the steps of increasing and lowering the frequency are combined, or the frequency may be only lowered or increased. lFurthermore, it is apparent that this invention is not limitedto wireless systems, and that thev sending and receiving antennae may be replaced by the sending and receiving conductors of a wired system.

While a local source of high 'frequency oscillations for changing the carrier frequency at the repeating station has been disbe understood that the inven- 4 be limited to this means, as it is obvious that the object of the invention may be accomplished by combining with the incoming carrier'current, energy in any form which will bring about al desired change in carrier frequency.

vAlthough this invention has been described as particularly applicableV to signaling systems, it is obvious that it may equally well be applied to other radio or conductive selective systems.

What is claimed is: 7

,1. The method of signal transmission which comprises combining modulated carrier oscillations with electrical energy of different characteristic and in selecting for transmission from the resultingoscillations modulated oscillations having a frequency differing from that of said carrier oscillations.

2. The method of signaling which comprises combining a modulated Wave of frequency f1 with a wave of the high frequency f2 and in selecting from the vresultant wave a component wave having differingy from f1 by the value f2. v

3. The method of relaying signals which consists in receiving a modulated wave, locally generating a high frequency Wave, combining said waves, and in selecting from the combined Waves and transmitting a modulated component Wave having a carrier frequency didering from that of the received modulated wave.

a carrier frequency 4. In a high frequency telephone repeating system, a receiving conductor adapted to rea genera r of osfor combining th- A received cillations, means 4modulated Wave and said oscillations so as to produce a resultant Wave, and means for selecting for transmission from said'resultant Wave a modulated wave component having a carrier frequency differing from that of said received wave.

5. I n a signaling system,'a sourceof modu` lated oscillations of frequency f1, a source of unmodulated oscillations of frequency f2, a

'distorting device, .means for supplying oscillations from bothsaid sources to said distorting device, and means for selecting from the resulting distorted oscillations, modulated Vmionic device having an input circuit and an output circuit, a source of modulated oscillations and a source of high frequency oscillations, means for supplying oscillations from both of said sources to said input circuit, and means for selectively transmitting' from said output circuit modulated oscillations having a carrier -frequenc differing from that of the oscillations supplied by said first named source.

8. In a system for relaying signals, the

combination of a thermionic device having an input circuit and an output circuit, a sourceof modulated osclllations and a source conductor -at each of said stations adapted to transmit the modulated oscillations ,of the l new frequency.

12. In a high sage, each of said stations comprising a conductor adapted to receive modulated oscillations of a frequency different from that of the modulated oscillations received by the adjacent stations, a source of high frequency oscillations at each of said repeating stations, the frequency supplied by each of said sources being different from that supplied by the sources at adjacent stations, means for com-- bining the generated oscillations at each of saidv stations with the received oscillations, each of said. combining means having associated therewith 'a conductor adapted to transmit a modulated wave having a frequency differing from that of the oscillations received at its respective repeating station.

13. The method of producing a modulated carrier Wave'having no unmodulated component 'of the vcarrier frequency which comprises, producing a pure modulated wave and ofhigh frequency oscillations, both of said /changing each of its instantaneous individual sources being adaptedto energize said input circuit, said output circuit constituting a source of modulated oscillations having a carrier frequency differing from the frequency of themodulated oscillations sup lied to said input circuit, and means for selectlvely amplifying they modulated oscillations duced by said last named source.

9. A plurality ofrepeating stations each comprising a conductor ,adapted toreceive a modulated Wave, means for'changing the frequency of the modulated Wave received at each of said stations, and aconductor at each of said stations adapted to transmit the modulated Wave of changed frequency.

10. A plurality of repeating-stations each comprising a conductor adapted to receive a modulated.4 Wave, a generator of high frequency oscillations at each of said repeating stations, the frequency supplied 'by each of said generators being different from that supplied by the generatorsat adjacent stations, means for combining the generated high frequency oscillations at each ofv said stations With the received oscillations, each of said combining means having associated therewith a conductor adapted to transmit a modulated wave having a frequency differing fromthat' of the received Wave. 11. In a high frequency signaling system,l the combination of a plurality of repeating stations adaptedto successivelyrepeat a message, each of said stations comprising aconductor adapted to receive modulated oscillations ofa frequency dierent from that of the modulated oscillations received by the ladjacent sta tions, means for changing the 'frequency of the received oscillations, and a frequency components thereof by a constant amount to produce a resultant modulated Wave of the desired carrier frequency.

14. The method of carrier transmission comprising modulating a carrier Wave, selecting atleast one component of the resulting energy, causing said selected energy to modulate a second carrier Wave and selecting at least one component of said modulated second wave. 15. TheV method of carrier transmission comprising modulating a carrier Wave, supand transmitting energy proportional to that of said third Wave.'

17. The method comprising combining tWo waves, selecting from the resulting energy asingle component having a frequency differing from that of one of said Wavesby the frequency of the other, causing said component to vary the amplitude of a third Wave transmitting energy proportional to that of said third'vvave, and -detecting said transmitted energy. f A l 18. The method of signaling comprising modulating a carrier Wave, suppressing all components except one side frequency component of the modulated carrier wave, and

Aof the resulting energy quency component, combining said side fresource of carrier oscillations, means causing this unsuppressed component to modulate a second carrier wave.

19. The method comprising varying the amplitude of a substantially constant frequency wave in accordance with a signal or control wave, suppressing all components except one side fresulting component, a carrier wave source,

the unsuppressed 4lating said second Wave in accordance means for causing said selected energy to modulate a wave supplied by -said carrier wave source, and means for selecting at least one component of said modulated carrier wave.

21. In a carrier transmission system, means for supplying a carrier wave, means for modulating said wave and for suppressing substantially all of the-unmodulated component of the carrier frequency, means for supplying a second carrier wave and for modulating said second wave in accordance with for suppressing substantially all of the component of one of the combination frequencies of said two carrier waves.

e 22. In a carrier transmission system, means for supplying a carrier wave, means for modulating said wave and for suppressing substantially all of the unmodulated component of the carrier frequency, means for supplying a second carrier wave and for moduwith the unsuppressed components resulting from the modulation of said first wave, means for suppressing substantially all of the coinponent of one of the combination frequencies of said two carrier waves, and means lfor transmitting the resulting energy to. a dis-v tant station. l

23. In combination, a combining device, means for impressing thereupon two waves of different frequencies, means for selecting from the resulting energy a single component having a frequency differing from that of one of said waves by the frequency of the other, means for` supplying a third wave, means for causing said selected component to vary the amplitude of said third wave, and means for transmitting energy proportional to that of said third wave.

24. An electrical system comprising acarrier wave source, means for modulating the Wavesupplied by said source and for suppressing all of the components of the moducomponents resulting from. p the modulation of said first wave, and means L lated carrier Wave except one side frequency component, a second carrier wave source, means for causing said unsuppiessed coinponent to modulate the wave supplied by saidsecond source, and suppressing' the un,- modulated component.

25. A transmitting station, a distant receiving station, means at said transmitting station totransmit modulated waves, an intermediate repeatlng station having a local source of waves, a combining device, means for impressing the modulated wave received j from said transmitting-station and waves v said received A corresponding` to the. received modulated waves detected by said device.

26. 'Ihe method of conveying signals transmitted by a high `frequency .wave comprisin independently,producingi another high rcquency wave, causingisaid waves to interact to produce a signal controlled wave of lower frequency than the transmitted wave, selectively receiving said signal controlled wave and acting upon said signal controlled wave to receive the signal comonent thereof. y

27. In a high frequency signaling system, means for receiving high frequency waves, means for combining said waves with locally generated waves of high frequency to produce waves of frequency lower than said received waves but of inaudible frequency,

means for amplifying said inaudible lower frequency waves, and means for deriving intelligible signals from said amplified waves.-

28. In a radio system, means for receiving a signal modified radiant energy wave of a given high frequency, means for combining therewith locally generated oscillations to produce va similarly modified wave of lower but inaudible frequency, means for amplifying said lower frequency wave, and means for detecting said amplified wave.

29. The method of high frequency signaling which comprises receiving high frequency carrier waves, combining therewith locally generated waves of greater energy -t0. produce beat frequency waves of higher than essential speech frequency, selecting said beaty frequency waves, and combining therewith other waves to produce intelligible signal waves of audio frequency.

30. The lmethod of radio signalingwhich comprises receiving carrier waves, combining l therewith locally generated vives to produce inaudible beat frequency waves of greater energy than the received waves, se-

lecting said inaudible waves, and combining therewith other waves to produce intelligible signal waves.

31. An electric Wave signaling system which comprises in tandem arrangement a 4plurality of groups of devices, each group constituting means for receiving a wave Whose frequency components are above essential speech frequencies', means for changing the frequency components by a locally predeterminedl amount to produce another wave Whose componeiit-s consist of/ other'` frequencies above essential speech frequencies, and means for conveying the produced wave to a succeeding point in the system.

32. The method which comprises combining high frequency waves with other waves to produce high frequency waves of a third frequency and combining waves with the waves of said third frequency to produce high frequency waves of'a frequency other than the waves of said third frequency or the Waves combined therewith, each'of said produced waves having a frequency above essential speech frequencies.

33. A radio signaling system vwhich comprises means for receivino` radiated carrier waves, means for combining therewith locally generated waves to produce inaudible beat fre uency waves, means for selecting said inaudible waves, and means for combining therewith other Waves to produce intelligible signal waves. v

34. The method of transmitting a modulated band of frequencies corresponding to one side band resulting from modulation to the exclusion of the unmodulated carrierfrequency and other side band components which consists in modulating in accordance with the signals to be transmitted a wave of frequency lower than said carrier frequency, selecting one of the side bands of said modulated wave to the eXclusionfof the other side band and the unmodulated component, and'modulating a wave of said carrier frequency in accordance with said selected band.

35. The method of transmitting a modulated band of frequencies corresponding to one side band resulting from modulation to the exclusion of the unmodulated carrier frequency and other side band components which consists in modulating in accordance with the signals to be transmitted a wave of :fre-l quency lower than said carrier frequency, selecting one of the side bands of said modulated wave to the exclusion ofthe other side band and the unmodulated component, modulating a wave of said carrier frequency 'in accordancewith said selectedy side band, and

selecting oneI side band of said modulated carrier frequency wave.

36.A carrier wave transmission system for producing a modulated band of frequencies corresponding to oneside band resulting from modulation to the exclusion of the unmodulated carrier frequency and other side band components, comprising means for modulating in accordance with signals to be transmitted a wave of frequency lower than said carrier" frequency, means for selecting tions for transferring the signal `from the received carrier wave to a carrier wave of lower frequency, said means'comprising a wave distorting device, a local souice of highfrequency current, and means for impressing the received carrier Wave and the locallygenerated current simultaneously upon said distorting device.

38. A radio transmitting system comprising a plurality of repeaters stations in tan:

dem arrangement and means at each of said stations for transferring thesignal fromthe received carrier wave to a carrier wave of higher frequency, wa've distorting device, a local source vof high frequency current, and means for impressing the received. carrier wave aiid the locally generated current simultaneously upon said distorting device. Y, l

39. A radio station for receiving and reradiating energy comprising a local source of high frequency waves, a' Wave distorting device at'said station, and means for simultaneously impressing on said wave distorting device waves from said high frequency source and carrier waves received at said repeater and means comprising a station, and means for impressing the result-A ant waves on a radiating conductor.

40. The method of indirectly amplifying high frequency electrical oscillatory energy which comprises combining said energy .with high frequency continuous electrical oscillat-ions of a frequency differing from s aid energy by a third readily-ampliiable high frequency, converting the combined energy by suitable' means to produce said. readilyamplifiable high Afrequency oscillations and am lifying said resulting readily-ampliiiable hgh frequency oscillations.

'41. The method of preventing the genera;

tion of undesired. oscillations in-a high frequencywave amplifying system which comrises impressing high frequenc aves to he amplified on Jthe input circuigfwthe system, converting the waves during amplification from one high frequency directly to another high frequency, and thereby producing A in the output circuit amplified high frequency waves of a frequency different from the f requency' applied to the input circuit and which the input circuit is not adjusted to receive efficiently.

42. The method of receiving lhigh frequency oscillations wherein the incoming energy is utilized to produce oscillations of a different locally predetermined frequency above good audibility which are then amphfied and transmitted to a conductive Wave transferring circuit.

43. The method of amplifyin and utilizing 'in a signaling system hig 1 frequency signal modulated oscillations wherein the oscillations are utilized to produce oscillations of a different locally predetermined high frequency which are then amplified and the resultant' amplified venergy further utilized as a carrier Wave in the signaling system.

44. The method of indicating carrier Wave repeating in a system operating to convert the energy of the'carriel1 wave from one carrier frequency to another by a thermionic frequency converting device which comprises producing indications by low frequency "components in the output-current from the converting device.

45. The method of impressing electrical energy representing a signal or message upon a transmitting medium, which consists in producing electric currents of different inaudible frequencies interacting to produce beats of inaudible frequency, controlling the energy to represent the signal or message to be transmitted, and impressing the beat energy upon the transmitting medium.

46. Transmitting apparatus comprising means for producing electric currents of different inaudible frequencies interacting to producel beats, means for controlling the energy to represent a signal or message, means for amplifying the beat energy, a transmitting medium, and 'means for impressing the amplified beat energy upon said transmitting medium.

47. Transmitting apparatus comprisingy means for producing electric currents of differentv inaudible frequencies mteractmg to producebeats, a transmitting medium, and a circuit intervening between saidmeans and said transmitting medium for selectively discriminating in favor of and transferring to a frequency intermediate said beat producing frequencies 48. The method of observing carrier Wave repeating in a system operating'to convertv the `energy of the carrier Wave from one carp Vtrier frequency to another which consists in l applying the carrier Waves to a frequency converting device together With other Waves to produce :modulated carrier Waves of a frequency different from the Waves to be converted, and observing low frequency signaling components in a circuit,coupled to the l converting device.

49. The method of amplifying high frequency,\electrical oscillatory energy which comprises combining the high frequency energy to be ampliiedwith other locally produced high frequency oscillations of 'a frey quency differing from the energy to be amplilied by a third readily-amplifiable high frequency, converting the combined energy by suitable means to produce oscillations of said readily-amplifiable highfrequency, selecting 4the energy of the third high frequency oscillations from other oscillations, and amplifying. the selected oscillations.

50. The method of producing a desired carrier Wave, modulated in accordance with Voice currents, from a carrier Waveof differ-` ent frequency modulated 1n accordance with 51.14 repeating system comprising thev combination of a highfrequency line adapted to receive a carrier wave of frequency p modulated in 'accordance with signals from a distant station, a vacuum tube device adapted to be supplied by said line and having an input circuit and an output circuit, means for,k tuning said input circuit to a signal Wave having the carrier frequency p, means for tuning said output circuitto a signal Wave having the carrier frequency 2p, and a high frequency line associated With said output circuit'.

In Witness whereof, I hereunto subscribe my name this 20th day of September, A. D.

. BURTON W. KENDALL. 

